Ubuntu – Extract a string from a line between positions given by a pattern in another line

command linetext processing

I'm looking to output the characters between two positions A and B that are specified by the preceding line. Per pair, the two lines are equal in length, but among pairs the lengths can vary. Is there an efficient way (huge file sizes) to do it with grep, sed, or awk?

Example file:

xxxxxxAxxxxxxBxxxxxx
1234567890MNOPQRSTUV
xxAxxxxxxxxxxxxxxBxxxxxx
1234567890MNOPQRSTUVWXYZ

…

I would like to obtain the output:

7890MNOP
34567890MNOPQRST

…

Best Answer

Using awk:

$ awk '!seen{match($0, /A.*B/);seen=1;next} {print substr($0,RSTART,RLENGTH);seen=0}' infile
7890MNOP
34567890MNOPQRST

Explanation: read in man awk:

RSTART
          The index of the first character matched by match(); 0 if no
          match.  (This implies that character indices start at one.)

RLENGTH
          The length of the string matched by match(); -1 if no match.

match(s, r [, a])  
          Return the position in s where the regular expression r occurs, 
          or 0 if r is not present, and set the values of RSTART and RLENGTH. (...)

substr(s, i [, n])
          Return the at most n-character substring of s starting at I.
          If n is omitted, use the rest of s.

Related Solutions

Ubuntu – Find out if lines of a file is sorted

#!/usr/bin/perl -w
use strict;

unless ( @ARGV == 1 && -f -r $ARGV[0] ) {
    die "Expected single file argument!\n";
}

my %cols;
my $ind = 0;

while (<>) {
    chomp;
    next if /^\s*($|#)/;
    ( @{ $cols{col1} }[$ind], @{ $cols{col2} }[$ind], @{ $cols{col3} }[$ind] ) = split;
    $ind++;
}

my @sorted1 = map { ${ $cols{col1} }[$_] } sort {
    ${ $cols{col1} }[$a] <=> ${ $cols{col1} }[$b] or
    ${ $cols{col2} }[$a] <=> ${ $cols{col2} }[$b] or
    ${ $cols{col3} }[$a] <=> ${ $cols{col3} }[$b]
} keys @{ $cols{col1} };
my @sorted2 = map { ${ $cols{col2} }[$_] } sort {
    ${ $cols{col1} }[$a] <=> ${ $cols{col1} }[$b] or
    ${ $cols{col2} }[$a] <=> ${ $cols{col2} }[$b] or
    ${ $cols{col3} }[$a] <=> ${ $cols{col3} }[$b]
} keys @{ $cols{col2} };

if ( "@sorted1" eq "@{ $cols{col1} }" and "@sorted2" eq "@{ $cols{col2} }") {
    print "File is sorted!\n"
}
else { print "File is unsorted!\n" };
__END__

If the columns are:

X1 Y1 Z1  
X2 Y2 Z2

Sort will be:

if (x1 > x2) then X1 Y1 Z1 > X2 Y2 Z2
if (X1 == X2) && (Y1 > Y2) then X1 Y1 Z1 > X2 Y2 Z2

To add more columns into the sort order, copy the pattern for the first two. I hope that's what you asked for.

Ubuntu – How to replace text between two patterns on different lines

It should work for you:

sed -e '/Security-Start/{ N; s/Security-Start.*Security-End/REDACTED/ }'

/Security-Start/ search for "Security-Start"
If you found it: "N;" means append the next line.
and do the replacements/Security-Start.*Security-End/REDACTED/ at the final result.

For more than of two line use this one:

sed -n '1h; 1!H; ${ g; s/Security-Start.*Security-End/REDACTED/p }'

Read here

Best Answer

Related Solutions

Ubuntu – Find out if lines of a file is sorted

Ubuntu – How to replace text between two patterns on different lines

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